According to the leaked audit, UKIP broke EU spending rules by spending money on polling during its general election campaign in 2015 and ahead of the EU referendum.

Business Insider has contacted UKIP for comment and will update when we hear back.

UKIP receives money from the EU as a member of "Alliance for Direct Democracy," (ADDE) a political grouping in the European Parliament where UKIP has several representatives. The money is meant to be spent on funding to promote the EU.

European Parliament rules prohibit the "indirect financing of a national political party" and funding "a referendum campaign."

The report says, according to Sky News: "The constituencies selected for many of the polls underline that the polling were conducted in the interest of UKIP."

"Most of the constituencies can be identified as being essential for reaching a significant representation in the House of Commons from the 2015 General Election or for a positive result for the 'Leave campaign'."

Referring to the EU referendum, it said: "Several pollings can be considered as financing of a referendum campaign which violates 8(4) ... prohibiting the financing of referenda campaigns."

"I've understood absolutely the rules," he said. "This is pure victimisation. I am the most investigated MEP in history. Look at what the pro-EU groups were spending."

Farage added that he accepts money was used to pay for polling during the general election, but he argues it was paid for by UKIP rather than the ADDE.

Regarding spending on the EU referendum, he said that all polling was paid for before the June vote, when he argues that different rules applied.

The audit puts the total misspend at £430,000 ($537,000), although some of that was misspent by other parties within ADDE, the audit said UKIP was responsible for the "lion's share."

A spokesman for the ADDE told Business Insider in an emailed statement they would take the matter to court, as they said auditors had "broadened the definition of 'expenditure supporting a political party.'"

He said: "The parliament administration has for months taken an aggressive and hostile attitude over the audit, amounting to nothing short of deliberate harassment.

"We have responded to their queries with a mass of information and explanation justifying our activities and expenditure. They have simply ignored our submissions and in several cases these submissions having been made repeatedly on their request," he said.

A spokesperson for the European Parliament told Business Insider that the audit was "standard procedure for European political parties and foundations."

She said that the European Parliament gives an annual grant to all European political parties which covers up to 85% of their spending. 80% of that is issued as an advance at the beginning of the year. When the year has ended, an accountant and the European Parliament finance team audit the expenses — which is the point at which UKIP were found to have misspent funds.

A party usually has 30 days back to pay back the money, and there is no suggestion that UKIP will face any punishment because there is no suspicion of fraud.